Method of shaping glass sheets to sharp bends

ABSTRACT

Simultaneously bending pair of glass sheets having a sharply bent portion extending across a portion of the sheet, using a combination of locally applied electrical resistance heating in said sharply bent portion in combination with general overall heating so that a pair of glass sheets bent simultaneously do not fuse together and can be separated after they are shaped, then assembled with a layer of plastic interlayer material therebetween and laminated.

United States Patent [1 1 J ansson et a1.

[ METHOD OF SHAPING GLASS SHEETS TO SHARP BENDS [75] Inventors: RobertA. Jansson, Pittsburgh;

Thomas J. Reese, Sarver, both of Pa.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[22] Filed: Mar. 29, 1972 [21] Appl. Nol: 239,032

[52] US. Cl 65/106, 65/273, 161/185 [51] Int. Cl C03b 23/02 [58] Field01' Search 65/103, 106, 107, 273; 161/35,

[56] References Cited UNITED STATES PATENTS Galey 65/273 1 1 Mar.5, 197411/1967 Barch 65/103 X 2/1959 Marini 65/107 X Primary Examiner-Arthur D.Kellogg Attorney, Agent, or Firm-Edward l. Mates; Thomas F. Shanahan[57] ABSTRACT Simultaneously bending pair of glass sheets having asharply bent portion extending across a portion of the sheet, using acombination of locally applied electrical resistance heating in saidsharply bent portion in com-' bination with general overall heating sothat a pair of glass sheets bent simultaneously do not fuse together andcan be separated after they are shaped, then assembled with a layer ofplastic interlayer material therebetween and laminated.

18 Claims, 6 Drawing Figures PAIENTED 3,795,501

SHEET 1 0F 2 HI HI METHOD OF SHAPING GLASS SHEETS TO SHARP BENDSBACKGROUND OF THE INVENTION This invention relates to fabricating shapedwindows, preferably of the type suitable for use as automobile windows.The present invention has been specifically utilized in connection withmaking V-shaped laminated Windshields in which a sharply bent portion ofthe installed windshield or backlight extends transversely of anelongated window from one longitudinal side edge thereof to its otherlongitudinal side edge. The V- shaped window is symmetrical about itssharply bent portion. The present invention is also suitable for use ina compound windshield or backlight or sidelight in which one region ofthe window is sharply bent into the roof of the vehicle in asubstantially horizontal plane I from another portion that extendsacross the front,

side, or rear of the vehicle. In addition, the present invention is alsosuitable for use in fabricating rearquarter windows for station wagonshaving a main portion extending forward of the vehicle from a sharplybent corner and a rear portion extending along the rear of the vehiclefrom the sharply bent corner.

In addition to automotive glass, the'present invention is also suitablefor use in bay windows for buildings which include a flat centralportion spaced outward from the frame of the building and angularlydisposed flat glass end portions extending inward from each end of thecentral portion. Other glass shapes having sharply bent portions arealso made possible by the present invention.

Various techniques have been developed to produce a windshield having asharply bent region. Various patents such as U. S. Pat. Nos. 2,11 1,392to Henry J. Galey; 2,176,999 to Robert A. Miller; 2,215,228 to James G.Oliver; and 3,248,195 to James S. Golightly and Harold E. McKelveysuggest various methods and apparatus employing electrical heaters forimparting a relatively sharp bend to a glass sheet. Furthermore, U. S.Pat. No. 2,871,623 to Herman R. Marini and U. S. Pat. No. 3,260,584 toAlfred E. Badger suggest using a heat absorbing material whichreradiates heat into a portion to be relatively sharply bent compared toother portions. The heat absorbing material is removed after the glassis shaped. Furthermore, it is also well known to bond electroconductivematerial onto a surface of a glass sheet in the form of an electricalresistance heating circuit. U. S. Pat. Nos. 2,557,893 to Cyril S.Linder; 2,569,773 to Leighton E. Orr; 2,648,752 to Arnold E. Saunders;2,648,754 to William O. Lytle; 2,710,900 to Cyril S. Linder; 2,877,329to Romey A. Gaiser; 2,993,815 to A. W. Treptow; 3,287,684 to AlbertArmbruster; 3,302,002 to Robert A. Warren; 3,467,818 to John D.Ballentine; and 3,484,583 and 3,484,584 to Hugh E. Shaw provide examplesof electroconductive heating circuits bonded to a surface of a ceramicor glass sheet. To the best of our knowledge, bus bars supplying currentto the electrical heating circuit are more electroconductive than theheating circuit in prior art circuits, even at portions connecting thebus bars to the circuit.

It has even been suggested in the prior art to groove the glass in theregion of sharp bending. U. S. Pat. Nos. 3,241,936 and 3,281,227 toHerbert A. Leflet, Jr. depict this technique. Such grooving weakens theglass.

Sharp localized bending has also been accomplished by bonding a heatreflecting coating on a portion of a surface opposite the surface facinga heat source. British Pat. No. 942,132 to George Hubble describes sucha method.

A method of localized heating using an electroconductive element bondedto a portion of a glass sheet surface is found in Canadian Pat. No.867,466 to Frie drich Jochim et al.

It has been found that heating circuits in the past have beeninterconnected between bus bars disposed along the opposite edges of theglass sheet. In the past, the bus bars have been of greaterelectroconductivity than that of the heating circuit elements in orderto be able to have the voltage supply as great a proportion of energy tothe heating elements with minimum loss of electrical energy to each busbar. Such prior art config urations supplied power at maximum efficiencyto the heating elements in the region where heat was desired.

In using a single elongated electroconductive heating strip with itsends connected to electrodes for applying electrical energy to heat theglass sheet locally along the line of the elongated strip ofelectroconductive material in the fabrication of V-shaped windows,sometimes breakage was experienced. The present invention provides amethod of reducing this breakage to a considerable extent.

SUMMARY OF THE INVENTION The present invention provides a windowcomprising a glass sheet having a sharply bent portion extending acrossa portion of the sheet with a shape necessary for a V-shaped windshieldusing a combination of overall heating of the glass sheet with a novelsetup of electrical resistance heating to accentuate heating in thesharply bent portion.

According to the present invention, the localized electrical resistanceheating is supplied by a pair of flexible strips of electroconductivematerial applied along the line of sharp bending. One of the strips ofelectroconductive material is applied between the glass sheets along theline of sharp bending. The other strip is applied parallel to the firststrip along the upper surface of the upper glass sheet so that a pair ofglass sheets and strips of electroconductive material may be assembledin bending relation to-an outline bending mold and electrodes broughtinto contact with the strips to apply electrical energy locally at theproper phase of the bending cycle. The flexible strips may be composedof removable material, such as metal strips, or of a more flexiblematerial such as carbon tape.

The resulting laminated window comprises two glass sheets conforming inshape and outline to one another with a layer of flexible plastic resinsuch as a polyvinyl acetal resin or a polyurethane resin adhering theglass sheets to one another in aligned relationship.

While the resulting laminated window described herein may be a V-shapedwindshield having a sharply bent portion extending across the width ofthe glass sheet to form two main portions symmetrically arranged withrespect to said sharply bent portion, the present invention is equallyadapted for any configuration of glass that incorporates a sharply bentportion extending completely across a glass sheet from one edge to anedge opposite thereto.

When both glass sheets have a strip ofelectroconductive material appliedalong a surface thereof, consider able improvement in the efficiency ofthe glass bending operation takes place. The arrangement of the presentinvention requires a lower voltage for localized heating, which preventsthe glass sheets from fusing to one another when they are bent as a pairwhile mounted in stacked, aligned relationship on a bending mold.

The use of a single, electroconductive heating strip arranged eitherbetween the glass sheets or along a surface of one sheet facing awayfrom the other sheet caused occasional breakage while bending glasssheets in pairs. The addition of a second electroconductive stripaligned with the first strip according to the present invention hasreduced the frequency of glass breakage.

The details of the present invention will be understood better in thelight of a description of illustrative preferred embodiments andvariations thereof that follows. In the drawings that form part of thedescription, like reference numbers refer to like structural elements.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of an assemblyof elements comprising parts of a V-shaped windshield showing how a pairof electroconductive strips are arranged rel ative to the glass sheetswhile shaping the pair of glass sheets according to one embodiment ofthe present invention;

FIG. 2 is an end elevation of the assembly of FIG. 1, taken along thelines lI-Il of FIG. 1 with the assembly turned slightly;

FIG. 3 is a top view taken along the lines III-III of 'FIG. 1 with theassembly turned slightly;

FIG. 4 is a fragmentary, enlarged, sectional view taken along the linesIV-IV of FIG. 1;

FIG. 5 is a view similar to FIG. 1, showing an alternate embodiment ofthe present invention; and

FIG. 6 is a fragmentary, enlarged, sectional view taken along the lineVI-Vl of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, referencenumber 10 refers to an assembly of elements comprising parts of aso-called V- shaped windshield having two main portions 12 and I4sharply bent with respect to one another along a transverse line ofsharp bending to which are applied thin elongated heating strips ofelectroconductive material 15 and 25. The windshield may also comprise apair of longitudinal end portions 18 and 20 that are bent with respectto their respective main portions 12 and 14. The windshield assemblycomprises an upper glass sheet 2] and a lower glass sheet 23 mountedwith their marginal edges comprising a top edge 22 and a bottom edge 24interconnected by end edges 26 and 28 in alignment.

The longitudinally extending electroconductive strips 15 and are appliedalong a portion of the flat glass sheets in parallel relation to oneanother along paths destined to become the sharply bent transverseportion between main portions 12 and 14 of the windshield. Strip 25 isapplied to the upper surface of glass sheet 23, then glass sheet 21 issuperimposed over glass sheet 23 with the strip 25 of electroconductivematerial disposed between glass sheet 21 and glass sheet 23. The

other strip I5 is applied to the upper surface of glass sheet 21. Eachof the strips 15 and 25 has an elongated extension portion extendingbeyond the opposite side edges of the windshield assembly for attachmentto an electrode 38. The latter are connected to a voltage source (notshown) through a switch (not shown) to control the application ofvoltage to heating strips 15 and 25.

The top edge 22, the bottom edge 24, and the end edges 26 and 28 of thewindow are constructed and arranged to conform within a frame of anautomobile windshield opening and, in a particular pattern for which thepresent invention was developed, has a sharp V-bend disposed centrallyacross the window from top edge 22 to bottom edge 24 such that the anglebetween main portion 12 and main portion 14 is I63- degrees at the topedge 22 gradually decreasing to 154 degrees at the bottom edge 24. Thewindshield is 32 inches wide at the sharply bent portion and each floatglass sheet is approximately mils thick.

Preferably, the heating strips of electroconductive material 15 and 25are thin, flexible metal strips having an electroconductivity per unitlength of between 0.01 and 0.25 ohms per inch. Particularly good resultsare obtained with a nichrome ribbon three-sixteenths inch wide, 0.005inch thick and having a resistance per unit length of 0.58 ohms per foot(or approximately 0.05 ohms per inch), although any conductive metal instrip form that does not tarnish readily and that does not become bondedto the glass or react chemically with the glass at the elevatedtemperature range needed for bending is acceptable.

The glass sheets with the electroconductive heating strip and additionalelectroconductive strip applied thereto is mounted on a bending mold ofan outline type and the glass supporting mold is subjected to anelevated temperature sufficient to heat the glass sheet to about thestrain point of the glass and to begin to soften the glass sheets. Whenthe glass reaches a suitable temperature in the vicinity of its strainpoint, voltage is applied along the elongated strips 15 and 25 toprovide more intense localized heat along the glass portion adjacent thethin elongated heating strips. This heating arrangement causes the glasssheet to develop a sharp bend extending across the glass sheet portionadjacent the elongated heating strips. Preferably, at the same time, therest of the glass conforms to the shape of an outline mold. However, ifthe bend is further complicated, as, for example, by the desire forbending the two main portions to complicated shapes, it may be necessaryto perform the shaping in more than one stage. Such multiple stagebending, if needed, is well known in the art and forms no part of thepresent in vention.

The conductive heating strips are preferably approximatelythree-sixteenths inch wide for use with glass sheets approximately 100mils thick that are presently used in laminated Windshields, when theelectroconductive elements are metal strips. Metal strips less thanone-eighth inch wide distort the glass and tend to fuse to the glassportion being bent sharply when sufficient electrical energy is suppliedto induce the sharp bending required locally. On the other hand, metalstrips one-fourth inch wide are not suitable for producing very sharpbends presently required.

Different glass sheet dimensions require different optimumcross-sectional areas for the heating strips to provide sufficientlocalized resistance heating. The strip must be sufficiently thin toavoid any optical distortion caused by the heating strip penetratinginto the heat-softened portion undergoing sharpest bending so that itflexes as the glass forms a V." In addition, the flexible metal stripsmust be sufficiently narrow so that the line of sharp bending is asnarrow as possible so that it does not become necessary to cover thesharply bent portion with an opaque coating of such a width that itinterferes with vision through the window. Presently, automobiledesigners are prepared to accept opaque coatings that hide any opticaldistortion or marking in the sharply bent portion of a V-shapedwindshield provided the coating has a maximum width of approximatelythree-eights inch.

in fabricating a laminated window, two aligned glass sheets 21 and 23with strips and 25 arranged as in FIGS. 1 to 4 are loaded forsimultaneous bending as a pair on a bending moldwith a parting materialto prevent fusion disposed therebetween. Electrodes 38 connected to asource of potential (not shown) are clamped to the extensions of strips15 and 25 to provide a pair of parallel heating circuits along the uppersurfaces of glass sheets 21 and 23.

If desired, either or both of the two heating strips 15 and 25 of theflexible metal may be replaced by a strip of conductive tape, such astape 19 on the upper surface of the upper glass sheet 21 and anadditional strip of conductive tape 29 on the upper surface of the lowerglass sheet 23. The two strips 19 and 29 of electroconductive tape haveextensions 31 at each end. The extensions are looped over the uppersurface of the upper glass sheet 21 to provide an area along the edgesof the assembly for clamping electrodes 38 against the conductive tapes.Such a system is depicted in FIGS. 5 and 6.

It is understood that it is not necessary to loop the extension 31 ofthe electroconductive tapes l9 and 29 around the edge of the upper glasssheet 21. They may both be looped about the edge of the lower sheet 23or each tape may be looped about a separate sheet or any combination ofloopings may be made at either end of each tape. An electrode 38 clampseach end of the looped extension against an exposed surface of the glasssheet-tape assembly.

One good feature of the flexible carbon tapes l9 and 29 is that sincecarbon tape is more flexible and has less density than a flexible metalstrip, carbon tape is less likely to penetrate into or otherwise markthe glass sheet on which it is applied. However, a flexible metal stripis reusable, whereas a carbon tape may be used only one time.

The two glass sheets with the parting material disposed between theiradjacent surfaces are supported in superimposed relation on an outlinebending mold of the gravity sag type and heated to an elevatedtemperature. The parting material is preferably of the type disclosedand claimed in U. S. Pat. No. 2,725,320 to Florian V. Atkeson and JamesS. Golightly, which need not be removed after bending. The outlinebending mold may be similar to that disclosed in U. S. Pat. No.2,999,338 to Ronald E. Richardson except for the difference in shape ofthe outline shaping surface and the substitution of clamping electrodesfor the resistance heaters, which electrodes are clamped as describedpreviously. When the temperature of the glass approximates its strainpoint, voltage is applied to the heating strips to assist the glass toassume the shape of the supporting mold. When the glass sheets haveconformed to the mold shaping surface, the two shaped glass sheets areremoved from the mold, separated from one another and laminated with athermoplastic material therebetween to form a complete windshield. Apreferable method of laminating glass to plastic is described in U. S.Pat. No. 2,948,645 to Laurence A. Keim.

Any well known commercial plate, float or sheet glass composition or anyother transparent glass generally used in windows is suitable for use inthe present invention. Particularly suitable compositions are thosePercent By Weight Na O l0 1 5 K 0 0-5 CaO 5-l 5 SiO 65-75 MgO 0-10 B 0;0-5

A typical soda-lime-silica glass suitable for use in accordance withthis invention has the following composition:

Percent by Weight 71.38 (usual variation 7l to 74%) SiO Na O 12.76(usual variation 12 to 14%) K 0 0.03 (usual variation 0 to l%) CaO 9.67(usual variation 8 to l2%) MgO 4.33 (usual variation 2 to 5%) Na SO 0.75(usual variation ().l to l.0%) Fe O 0.15 (usual variation 0.] to l.0%)AI O 0.8l (usual variation 0.l to 1.0%)

The plastic layer of a laminated window is selected from those materialswhich are flexible, optically transparent and, for bilayer Windshields,are somewhat abrasion resistant. Further, the plastic materials, whenlaminated to a thin ply of glass to form a laminated window, shouldminimize the dangers of both lacerative and concussive injuries. Tofulfill these latter two requirements, the plastic inner layer materialis preferably a polyurethane resin or a polyvinyl acetal resin. Typicalsuitable polyurethane resins of the thermosetting type are described andclaimed in U. S. Pat. No. 3,509,0l5 to Marco Wismer, Vernon G. Ammonsand Michael E. Dufala, while suitable polyurethane resins of thethermoplastic type are described in U. S. Pat. application Ser. No.155,944, filed June 21, 1971, the disclosure of which is incorporatedherein by reference. A typical polyvinyl acetal resin is described in ULS. Pat. No. 2,400,957 to Stamatoff. More details on the preparation ofpolyvinyl acetal resins are found in U. S. Pat. No. 2,496,480 and U. S.Pat. No. Re 20,430. Various plasticized polyvinyl acetal resins aredescribed in U. S. Pat. No. 2,372,522 and many well-known plasticizersfor polyvinyl butyral are found in U. S. Pat. No. 2,526,728 to Burk etal.

The inner plastic ply is of uniform thickness from about 10 to 75 milsthick, but is preferably about 20 to 50 mils in thickness. Inner plasticplies of less than 10 mils in thickness are not recommended because thinplastic sheets of less than 10 mils thickness tear easily TABLE IIDETAILS OF BENDING TRIALS Initial Power Time 60 Number and LehrApplication Power Cycle Maximum Peak Composition Temperature TemperatureApplied A.C. Current Power of Strips (F.) (F.) (Seconds) Volts (Amperes)(Watts) IE 800 930 480 X 13 X ID 800 960 600 31% I0 3 I3 I F. 800 )60765 34 I0 340 ID 800 960 540 33 I25 413 2]) R00 805 24 I7 408 IC 800 960895 36 720 Ill X X 87] 49.7 20 994 IE X X 675 52.2 I3 679 lAy 800 985805 64.5 I5 968 2A 800 985 655 37 20 740 1A 800 985 675 53 I 663 lAy 800985 710 55% 12.5 691 IE 800 960 755 32.5 14.5 471 Notes: X not availabley top plate broke upon impact. Tearing decreases penetration resistanceof the laminated structure, which presents the danger in a motor vehicleof an occupant being partially or completely ejected in an accident.Inner plastic plies of greater than 75 mils in thickness should not beused because they result in a more rigid laminated structure whichincreases the danger of concussive injuries upon heat impact. Also,thicker plastic plies increase the weight of the resultant laminatedstructure and reduce light transmittance.

The following compositions can be used as heatingstrips: nichromeribbon, copper ribbon or braid, metal alloy ribbon, stainless steeltape, carbon tape, and the like.

The following compositions were actually used to bend pairs of glasssheets into V-shaped configurations. Table l recites the construction ofthe strips.

wide, thick EXAMPLES The following examples report several experimentseach case. In some cases, an additional strip was applied over theupward facing surface of the upper glass sheet. Electrodes wereconnected to the ends of either the single strip or to the correspondingends of the pair of strips to form two heating circuits arranged inparallel along the heating strips applied to the glass surfaces.

The glass-laden mold was introduced into a lehr maintained at a lehrtemperature recorded in Table II. A thermocouple attached to the upperglass sheet surface about three to four inches from the heating stripand approximately midway between the side edges of the attached glasssheet recorded the glass temperature. When the recorded temperaturereached a value listed as power application temperature, 60 cyclealternating current was applied between the electrodes at a recordedvoltage for a period of seconds listed in Table I]. The resultingmaximum current in amperes and peak power in watts for each run is alsotabulated in Table II. After bending was completed, the bent sheets werannealed by controlled cooling.

From the above results, it becomes apparent that less voltage isrequired to produce the sharp bend when two parallel heating circuitsare used than when one heating strip is used. Furthermore, using twoheater strips lessens the chance of glass breakage. In addition, whenthe electric power supplied does not exceed 50 watts per inch of lengthof said sharply bent portion, less breakage occurs.

A pleasant surprise discovered from this work is that a high voltage isnot needed to impart a sharp bend to one or more glass sheets. In thepast, thousands of volts have been applied along strips ofelectroconductive material applied to a glass surface to shape theglass. These experiments demonstrate that electric heat needed forV-shaped bends in glass can be obtained from ordinary line current fromI I0 volts A.C. or 220 volts A.C. using a step-down transformer. Thelower voltage applications are safer for operating personnel to handleand reduce the load required of a local power system.

Also, in order to minimize glass breakage, it is recommended that thevoltage be applied initially at a low value. The voltage can then beincreased to a maximum value not exceeding line voltage, either by agradual increase or by a stepwise increase.

The form of the invention shown and described in this disclosurerepresents an illustrative preferred embodiment and certainmodifications thereof. It is understood that various changes may bemade, such as applying an additional strip of electroconductive materialacross the lower surface of the lower sheet provided suitableprecautions are taken to insulate the additional strip from a groundingconnection through the metal mold, whereby the electrodes can be clampedto provide three parallel heating circuits, for example, as well asother changes that will become apparent from reading this specification,without departing from the gist of the invention as defined in theclaimed subject matter that follows. It is also understood that each ofa pair of glass sheets bent simultaneously to a V-shaped configurationmay be laminated separately to a layer of plastic resin to form abilayer window consisting essentially of a layer of glass facingoutwardly of a vehicle in which the bilayer window is installed and alayer of plastic resin facing inwardly.

We claim:

1. In the method of bending a glass sheet to a shape comprising asharply bent portion including applying against said portion to besharply bent a narrow, elongated strip of electroconductive material,heating said glass sheet to a minimum temperature approximating itsstrain point and applying additional heat to said portion by applyingelectric power to said strip while said glass sheet is at least atapproximately its strain point, the improvement comprising applyingagainst said portion to be sharply benta strip of electroconductivematerial which is between about one-eighth inch wide and aboutone-fourth inch wide, applying a voltage across said strip of amagnitude such that the electric power applied to said strip does notexceed 50 watts per inch of length, and bending the glass sheet in theheated portion thereof.

2. In the method according to claim 1, the improvement wherein saidvoltage does not exceed 220 volts.

3. In the method as in claim 1, the improvement wherein said treatmentis applied simultaneously to two glass sheets while the latter aresupported in bending relation to a glass sheet bending mold.

4. In a method of bending a pair of glass sheets simultaneously to asharp bend wherein one portion of each said glass sheet is bent sharplywith respect to another portion of said glass sheet along a line ofsharp bending extending from edge to edge of said glass sheet andaligned with a corresponding line of sharp bending in said other glasssheet, by a combination of general heatingsupplemented by localizedelectric heating induced from a strip of electroconductive materialdisposed between the sheets in a region intersecting said lines of sharpbending and wherein said glass sheets are mounted in pairs in alignedrelation to one another on a mold, the improvement comprisingsuperimposing an additional strip of electroconductive material on theupper surface of the upper glass sheet of said pair in said region ofsharp bending, each of said strips of electroconductive material beingbetween about oneeighth inch wide and about one-fourth inch wide,simultaneously applying electrical power along the length of each ofsaid strips of a magnitude such that the electrical power applied toeach said strip does not exceed watts per inch of length, and bendingsaid pair of glass sheets in the heated region thereof.

5. In the method as in claim 4, the improvement wherein at least one ofsaid strips is comprised of a flexible metal capable of reuse in bendingadditional pairs of glass sheets.

6. In the method as in claim 4, the improvement wherein at least one ofsaid strips is comprised of a carbon tape.

7. In the method as in claim 4, the improvement wherein said electricpower is applied at a voltage that does not exceed 220 volts.

8. In combination with the method as in claim 4, the additional steps ofremoving said bent sheets from said mold and laminating them to oneanother with a layer of plastic resin therebetween.

'9. In the method as in claim I, the improvement wherein said strip iscomprised of a flexible metal capa ble of reuse in bending an additionalglass sheet.

10. In the method as in claim 1, the improvement wherein said strip iscomprised of carbon tape.

11. In the method as in claim 1, the improvement wherein said strip iscomprised of nichrome ribbon.

12. In the method as in claim 4, the improvement wherein at least one ofsaid strips is comprised of nichrome ribbon.

13. In the method as in claim 1, the improvement wherein said strip hasa resistance of up to about 0.25 ohms per inch.

14. In the method as in claim 4, the improvement wherein each of saidstrips has a resistance of up to about 0.25 ohms per inch.

15. In the method as in claim 1, the improvement which comprisesremoving said strip after said glass sheet is bent.

16. In the method as in claim 4, the improvement which comprisesremoving said strips after said glass sheets are bent.

17. In the method as in claim 15, the improvement wherein said strip iscapable of reuse in bending an additional glass sheet.

18. In the method as in claim 16, the improvement wherein said stripsare capable of reuse in bending additional pairs of glass sheets.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 'inventork's)Robert A. Jameson and Thomas J. Reese It is certified that error appearsin the above-identified patent ahd that said Letters Patentare herebycorrected as shown below:

Abstract of the Disclosure, line 1, after "bending" please add a.

Column 1, line 50, please charige "2,557,893" to --2,557,9s3--.

Coluinn 7, Table I, last line, after "wide," please add 010 inch.

Column 8, lines 1 and 2, please delete the word "simultaneusly.

Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 6O376-P69 us GQVERNMENY PRINTING OFFICE: I969o-ses-aaa.

FORM PC4050 (10-69)

2. In the method according to claim 1, the improvement wherein saidvoltage does not exceed 220 volts.
 3. In the method as in claim 1, theimprovement wherein said treatment is applied simultaneously to twoglass sheets while the latter are supported in bending relation to aglass sheet bending mold.
 4. In a method of bending a pair of glasssheets simultaneously to a sharp bend wherein one portion of each saidglass sheet is bent sharply with respect to another portion of saidglass sheet along a line of sharp bending extending from edge to edge ofsaid glass sheet and aligned with a corresponding line of sharp bendingin said other glass sheet, by a combination of general heatingsupplemented by localized electric heating induced from a strip ofelectroconductive material disposed between the sheets in a regionintersecting said lines of sharp bending and wherein said glass sheetsare mounted in pairs in aligned relation to one another on a mold, theimprovement comprising superimposing an additional strip ofelectroconductive material on the upper surface of the upper glass sheetof said pair in said region of sharp bending, each of said strips ofelectroconductive material being between about one-eighth inch wide andabout one-fourth inch wide, simultaneously applying electrical poweralong the length of each of said strips of a magnitude such that theelectrical power applied to each said strip does not exceed 50 watts perinch of length, and bending said pair of glass sheets in the heatedregion thereof.
 5. In the method as in claim 4, the improvement whereinat least one of said strips is comprised of a flexible metal capable ofreuse in bending additional pairs of glass sheets.
 6. In the method asin claim 4, the improvement wherein at least one of said strips iscomprised of a carbon tape.
 7. In the method as in claim 4, theimprovement wherein said electric power is applied at a voltage thatdoes not exceed 220 volts.
 8. In combination with the method as in claim4, the additional steps of removing said bent sheets from said mold andlaminating them to one another with a layer of plastic resintherebetween.
 9. In the method as in claim 1, the improvement whereinsaid strip is comprised of a flexible metal capable of reuse in bendingan additional glass sheet.
 10. In the method as in claim 1, theimprovement wherein said strip is comprised of carbon tape.
 11. In themethod as in claim 1, the improvement wherein said strip is comprised ofnichrome ribbon.
 12. In the method as in claim 4, the improvementwherein at least one of said strips is comprised of nichrome ribbon. 13.In the method as in claim 1, the improvement wherein said strip has aresistance of up to about 0.25 ohms per inch.
 14. In the method as inclaim 4, the improvement wherein each of said strips has a resistance ofup to about 0.25 ohms per inch.
 15. In the method as in claim 1, theimprovement which comprises removing said strip after said glass sheetis bent.
 16. In the method as in claim 4, the improvement whichcomprises removing said strips after said glass sheets are bent.
 17. Inthe method as in claim 15, the improvement wheRein said strip is capableof reuse in bending an additional glass sheet.
 18. In the method as inclaim 16, the improvement wherein said strips are capable of reuse inbending additional pairs of glass sheets.